1. Technical Field
This invention relates to a tapered roller bearing which can be assembled without the need for the steps of bottom expanding of the retainer and caulking of the retainer.
2. Background Art
A typical tapered roller bearing includes an inner race having a tapered raceway on its outer periphery, an outer race having a tapered raceway on its inner periphery, a plurality of tapered rollers disposed between the raceways of the inner and outer races so as to be circumferentially spaced apart from each other, and a retainer keeping the tapered rollers spaced apart from each other.
Retainers used in this type of tapered roller bearing include resin retainers, which are frequently used in bearings for automobiles, and pin type retainers (which are in the form of a plurality of pins inserted through holes formed in the respective tapered rollers to retain the tapered rollers), which are used in extra-large bearings used to support e.g. spindles of windmill generators. But other than these retainers, most retainers used in tapered roller bearings are in the form of iron plates.
JP Patent Publication 2001-50281A discloses an iron plate retainer. This iron plate retainer is a conical member located radially outwardly of a pitch circle that passes through centers of the respective tapered rollers and having a plurality of circumferentially spaced apart pockets in which the respective tapered rollers are received. The pockets are all identical in shape. The tapered rollers are all identically shaped too. The inner race has a large flange at the large-diameter end of its raceway which supports axial loads that act on the tapered rollers, and a small flange at the small-diameter end of its raceway which prevents separation of the tapered rollers from the inner race.
The separately prepared retainer, tapered rollers, inner race and outer race are assembled into the tapered roller bearing of JP Patent Publication 2001-50281A in the following manner. The tapered rollers are inserted into the respective pockets of the retainer from radially inside of the retainer. Since the pockets are narrower than the diameter of the tapered rollers, once fitted in the pockets, the tapered rollers are retained in the pockets without radially outwardly separating from the retainer.
The inner race is then axially inserted into the retainer. If, in this state, the roller inscribed circle of the tapered rollers fitted in the retainer is smaller in diameter than the outer diameter of the small flange of the inner race, the small flange of the inner ring interferes with at least one of the tapered rollers, making it impossible to insert the inner race into the retainer. Thus, in order to prevent the small flange of the inner race from interfering with at least one of the tapered rollers, it is necessary to radially expand the small-diameter end of the retainer beforehand.
In particular, using a presser and bottom expanding die, the small-diameter end portion of the retainer is plastically deformed radially outwardly (this step is hereinafter referred to as “bottom expansion”) such that when the tapered rollers are fitted in the retainer, the roller inscribed circle has a larger diameter than the outer diameter of the small flange of the inner race.
The tapered rollers are fitted in, and then the inner race is inserted into, the thus bottom-expanded retainer. Then, using the presser and a caulking die, the small-diameter end portion of the retainer is plastically deformed radially inwardly until the retainer returns to its original shape, i.e. until the diameter of the roller inscribed circle of the tapered rollers becomes smaller than the outer diameter of the small flange of the inner race (this step is hereinafter referred to as “caulking”). Thus after caulking, the inner race cannot slip out of the retainer. Thus, the subassembly of the inner race, tapered rollers and retainer are complete, in which the respective components are securely coupled together. As a final step, this assembly is fitted in the outer race to complete the tapered roller bearing.
It is necessary to prepare plural different bottom expanding dies and caulking dies for retainers having different model numbers and thus having different diameters and/or different number of pockets. This has been a major cause of increased manufacturing cost of conventional tapered roller bearings.
In order to bottom-expand a retainer of a different model number, it is necessary to change the bottom expanding die set in the presser to a new one and adjust it. In order to caulk a retainer of a different model number too, it is necessary to change the caulking die set in the presser to a new one and adjust it. A long time is needed for such die change and adjustment. Before caulking a retainer of a different model number, it is necessary to set the bottom dead center of the presser using an extra retainer. This extra retainer cannot be used in an actual bearing.
If the retainer, tapered rollers and inner race are configured such that when the tapered rollers are fitted in the retainer, the roller inscribed circle has a diameter equal to or smaller than the outer diameter of the small flange, it is possible to omit the bottom expanding and caulking of the retainer. In this arrangement too, once the tapered roller bearing is mounted between a shaft and a housing, the tapered rollers can never move over the small flange of the inner ring, separating from the bearing because the bearing interior space is sufficiently small in this state. But in the state of the subassembly of the inner race, tapered rollers and retainer, the inner race could slip out of the retainer, disintegrating the subassembly.